Better document where project paths (starting with `/` to get to project root) can be used

Discussed in https://github.com/quarto-dev/quarto-cli/discussions/3784

^{Originally posted by edalfon December 29, 2022}
Hi,

We use includes to re-use content across documents in a Quarto website project.

In this project, we set the option execute-dir: project to keep the working directory for computations pinned to the root directory of the project. That way, for example, all documents can refer to ./data/fancy_data, regardless of which subfolder they are placed in. For us this is important because we organize the content of the project in a bunch of subfolders that can go nested to different depth. Without the execute-dir: project the project would simply be much harder to mantain and keep track of the paths we should use in each document.

We expected {{< include >}} to follow the same project's execute-dir option, but it doesn't seem so. Instead, it always resolves to the same folder of the file you are including content in. So if you are in a subfolder and whant to include some content in the root of the project, you cannot do this {{< include _codebit.qmd>}}, but you have to do something like this {{< include ../../../_codebit.qmd>}}. And the ../../... part would depend on where the document lives and if you decide to reorganize the structure of the documents, you would need to update that as well. So, it is a bit of a mess.

We couldn't find a way around this or any other option similar to execute-dir, but for the whole working directory of the project and not only for computations.

Wouldn't it be better to have the includes directive to follow the execute-dir option?, is there currently any way to do it?